The invention generally relates to nucleic acids and polypeptides encoded therefrom. More specifically, the invention relates to nucleic acids encoding membrane bound and secreted polypeptides that are homologous to thymosin, fibromodulin and ephrin-type A receptors, as well as vectors, host cells, antibodies, and recombinant methods for producing these nucleic acids and polypeptides.
Beta-thymosins are a family of related peptides that were first isolated from calf thymus, but are known to be present in a wide variety of mammalian and other vertebrate cells and tissues. Thymosin-beta-4 (TMSB4) was the first member of the family to be characterized, and was proposed to be a thymic hormone acting at early stages of T-cell maturation. However, the high concentration of the protein and presence of its mRNA in a number of other tissues and cells, in addition to the lack of an identifiable secretory signal sequence, suggested a more generalized function in many cell types. This was confirmed by findings that TMSB4 forms a 1:1 complex with G-actin in blood platelets (A. Weber et al., “Interaction of thymosin beta 4 with muscle and platelet actin: implications for actin sequestration in resting platelets,” 31(27) Biochemistry 6179-85 (1992)).
Thymosin-beta-10 is related closely to TMSB4 in sequence and is also an actin-sequestering protein. mRNA species of similar molecular weights encoding TMSB10 are found in most tissues of rats, although Lin and Morrison-Bogorad (1991) identified TMSB10 mRNA of higher molecular weight in the testes of sexually mature rats. The latter differs from the more ubiquitous form only in its 5′-untranslated region, beginning 14 nucleotides upstream of the translation initiation codon. This finding, together with primer extension experiments, suggested that the two mRNA types are transcribed from the same gene through a combination of differential promoter utilization and alternative splicing. Both mRNAs are found in pachytene spermatocytes; only testes-specific mRNA is detected in postmeiotic haploid spermatids. Immunohistochemical analysis shows that the protein was present in differentiating spermatids, which suggests that testes-specific TMSB10 mRNA is translated in haploid male germ cells. Immunoblot analysis using specific antibodies indicates that TMSB10 synthesized in adult testes is identical in size to that made in the brain (S. C. Lin et al., “Cloning and characterization of a testis-specific thymosin beta 10 cDNA. Expression in post-meiotic male germ cells,” 266(34) J. Biol. Chem. 23347-53 (1991)).
Ephrin receptors comprise the largest known family of receptor protein tyrosine kinases. They have been implicated in mediating developmental events, particularly in the nervous system. Receptors in the ephrin subfamily typically have a single kinase domain and an extracellular region containing a Cys-rich domain and two fibronectin type III repeats. Along with their ligands, called ephrins, they play important roles in neural development, angiogenesis, and vascular network assembly (9(4) Mol. Cells, 440-5 (1999 Aug. 31)).
Fibromodulin is a member of a family of small interstitial proteoglycans that also includes decorin, biglycan and lumican. The proteoglycans bind to other matrix macromolecules and thereby help to stabilize the matrix. (Buckwalter et al., 47 Instr. Course Lect 477-86 (1998)). It is speculated that they may influence the function of chondrocytes and bind growth factors. Proteoglycan protein cores are structurally related and consist of a central region of leucine-rich repeats flanked by disulfide-bonded terminal domains. Fibromodulin has up to 4 keratin sulfate chains within its leucine-rich domain. It enjoys wide tissue distribution and is most abundant in articular cartilage, tendon and ligament. It has been suggested that fibromodulin participates in the assembly of the extracellular matrix by virtue of its ability to interact with type I and type II collagen fibrils and to inhibit fribrillogenesis in vitro. Sztrolovics et al. cloned the 3′-untranslated region of fibromodulin cDNA, and used it to map the gene by fluorescence in situ hybridization (FISH) to 1q32 (Sztrolovics et al., 23 Genomics 715-7 (1994)). This localization to chromosome 1 has since been confirmed by PCR analysis of somatic cell hybrids.